Electric motor with hollow rotor and method of fabricating the hollow rotor

ABSTRACT

An electric motor with a hollow rotor is described whose armature winding is arranged on an extremely thin-walled tubular winding support. The stationary ferromagnetic core of the hollow rotor and the likewise ferromagnetic core of the exciting winding are equipped with cooling channels through which, e.g., water is fed for removal of the heat produced by the electric current. The hollow rotor, which is arranged on the armature shaft so as to be displaceable by means of a sliding sleeve can be slowed down by means of an electromagnetic braking device in such a way that the forces generated by a spring and an electromagnet in the direction of the armature shaft are transferred to the hollow rotor by a disk attached to the sliding sleeve. The braking areas used are parts of the inside wall of the winding support which has a cylindrical or conical shape. Moreover, a method of fabricating a hollow rotor is described.

Waited States Patent [191 Biiscli et a1.

[451 May 22, 1973 [75] Inventors: Lothar Biisch, 755 Rastatt; Hans-Joachim Blocher, 7418 Metzingen, both of Germany [73] Assignee:Gesellschoft Fur Kernforschung mbH, Metzingen, Germany 22 Filed: Nov.27, 1970 21 Appl.No.:93,374

[30] Foreign Application Priority Data Nov. 26, 1969 Germany ..P 19 54280.4

[52] US. Cl. ..310/266, 310/54, 310/77 [51] int. Cl. ..H02k 1/22 [58]Field of Search ..310/266, 77, 67, 310/44, 54, 61, 26, 49 R [56]References Cited UNITED STATES PATENTS 2,102,409 12/1937 Faus ..310/26UX 3,418,505 12/1968 Mihalko et a1. ..310/266 3,479,539 11/1969 Brion..310/49 3,356,877 12/1967 Burr 310/266 3,312,846 4/1967 Baudot 310/2662,944,169 7/1960 Schmidt ..310/266 1,796,556 3/ 1 931 Boitel ..310/266 X768,982 8/1904 Duncan ....310/266 UX 3 ,329,846 7/1967 Lawrenson..310/266 2,987,637 6/1961 Bertsche et al ..310/266 X 3,148,294 9/1964Jaeschke ..310/266 X 2,677,256 5/1954 Donandt.... ..310/77 X 3,480,81011/1969 Potter ....310/61 X 3,439,201 5/1969 Levy et 3.1.. ....310/61 X2,694,781 11/1954 Hinz ..310/77 2,727,163 12/1955 Meyer ..310/77 PrimaryExaminer-.1. D. Miller Assistant Examiner-Mark O. Budd Attorney-Spencer& Kaye [57] ABSTRACT An electric motor with a hollow rotor is describedwhose armature winding is arranged on an extremely thin-walled tubularwinding support. The stationary ferromagnetic core of the hollow rotorand the likewise ferromagnetic core of the exciting winding are equippedwith cooling channels through which, e.g., water is fed for removal ofthe heat produced by the electric current. The hollow rotor, which isarranged on the armature shaft so as to be displaceable by means of asliding sleeve can be slowed down by means of an electromagnetic brakingdevice in such a way that the forces generated by a spring and anelectromagnet in the direction of the armature shaft are transferred tothe hollow rotor by a disk attached to the sliding sleeve. The brakingareas used are parts of the inside wall of the winding support which hasa cylindrical or conical shape. Moreover, a method of fabricating ahollow rotor is described.

14 Claims, 4 Drawing Figures 4 Sheets-Sheet 1 Fig.1

Lorhor Bosch Hons-do0chirn Blocher ATTORNEYS.

INVENT ORS.

Patented May 22, 1973 4 Sheets-Sheet 2 R Om mm vw RN 2 INVENTORS.

Lothor Bdsch Hons-Joachim Bloc-her %ww BY ATTOR NEYS Patented May 22,1973 3,735,174

4 Sheets-Sheet 5 Schnilf A-A INVENTORS.

Loihor Bsch Hons-Joachim Blocher ATTORNEYS.

Patented May 22, 1973 4 Sheets-Sheet 4 INVENTORS.

Lothor B'cisch Hons- Joachim Blocher I ATTORNEYS.

ELECTRIC MOTOR WITH HOLLOW ROTOR AND METHOD OF FABRICATING THE HOLLOWROTOR BACKGROUND OF THE INVENTION The invention relates to a DC motorwith hollow rotor for'the generation of high nominal torques and highaccelerations at low moment of gyration.

These motors are required especially for electrical drives withextremely fast startup and slowing down actions, e.g., as servo-motorsin measurement and control systems where high efficiencies and minimumdimensions are needed and, a t'the same time, only a low moment ofinertia is to be overcome in the case of a sepa rate drive.

It is known (catalog DC Mikromotoren 'of'Dr. Faulhaber company,Feinmechanische Werkstatten, 7036 Schonaich/Wurtt., Germany) that theserequirements can be fulfilled by keeping the-weight of the armature lowthrough separating the armature winding from the ferromagnetic armaturecarrying the magnetic flux. In this type of ironless hollow rotor thewinding is cast in a synthetic resin plastic or the like and connectedwith the armature shaft through a disk. I

The fact that the winding treated with synthetic resin must itself beused to transmit the torque results in three specific disadvantages: Themechanical stability of the assembly is limited, and influences oftemperature and mechanical oscillations may give rise to temporary orpermanent deformations of the winding. This necessarily requires a widerair gap which, in turn, results in either more expense for excitation ora decrease of power. The temperature carrying capacity, which is limitedfor mechanical reasons, at the same time implies a limit to the currentcarrying capacity and, hence, to power.

The same disadvantages are inherent in the ironless hollow rotor ofanother well-known motor which is described in the Honeywell catalogServomotor l-ISM" datedNov., 1968.

SUMMARY OF THE INVENTION rotor and the winding support being designed asan extremely thin-walled tube.

The tubular winding carrier makes for high stability of shape of thehollow rotor which allows smaller air gaps to be achieved throughmaintaining closer toler-' ances in the fabricating process at lessexpenditure. in addition, the ratio between torque and magnetic fluxwill increase with decreasing sizeof the air gap.

To connect the winding support with the armature shaft, the windingsupport is designed as a flange on at least one side. If a rotor has alength diameter ratio in excess of two to one, it is advisable toconnect both sides of the rotor to the shaft.

If only one side of the winding support is connected to the shafttransmitting the. torque, magnetic return will be made in a well-knownway through a free standing hollow cylindrical armature core extendinginto the hollow'rotor and made of a material of high relativepermeability with low eddy current losses. In the case of smaller rotordiameters it may be useful to connect the winding support to the frontside of a shaft butt and fill the bore of the hollow rotor with astationary cylindrical or hollow cylindrical armature core for magneticreturn.

The invention also servespurpose of attaining the maximum possiblecurrent carrying capacity of the armature winding and the excitingwinding so that apredetermined motor power is achieved with a minimum ofcopper and, hence, low mass.

In the invention, this is achieved by an electric motor consisting of ahollow rotor with a tubular winding support frictionally connected withthe armature schaft, a ferromagnetic armature core for magnetic returnwhich at least partly fills the bore of the hollow rotor and is firmlyattached to the motor casing, and of devices for removal of the heatproduced by the electric current from at least one of the componentsadjacent to the exciting and armature windings, the armature core of thehollow rotor and the ferromagnetic core of the exciting winding(exciting core). These devices may consist, e.g., of cooling channelsarranged in the armature core and the exciting core and through whichwater is ducted as the coolant.

In this case, it is advantageous totarrange bores'on the periphery ofthe hollow cylindrical armature core extending in the direction of itslongitudinal axis which are divided into two groups of channels on thefront side which is connected with the bearing plate, byone channel forintroducing a coolant and extending mainly on the level of the frontface, and another channel situated on the same level for removing acoolant, which two groups of channels are interconnected within eachgroup and connected with each other by a third channel on the otherfront side. I

It may be advantageous for an exciting core with a cylindrical outsideto have cooling channels arranged on its periphery'in the way of athread with at least two courses at a predetermined pitch in such a waythat the coolant flows in through a first course and back in a secondcourse. In this arrangement, the inlet for the coolant is connected toafirst course of the cooling channels on'a front side of the excitingcore and the outlet of the coolant is connected to a second course onthe same front side and both courses are connected with each otheron'the other front side so that the coolant can flow through the coolingchannels from the inlet to the outlet.

Another purpose of the invention is the development of anelectromagnetic braking device which can function without any increasein mass of the hollow rotor.

In the invention, this problem is solved byan electric motor consistingof a hollow rotor with a tubular winding support, a sleeve arranged onthe armature shaft so as to be axially displaceable (sliding sleeve) towhich the hollowrotoris firmly attached and an electromagnetic devicefor displacing the hollow rotor on the armature shaft from its firstposition (operating position) to another position (brakingposition)where, in the brakingposition, a surface of the winding support iscontacted with part of the surface of the free standing armature coreacting as a braking area.

In this design, the elctromagnetic device for displacing the hollowrotor consists essentially of a ferromagnetic disk which is so connectedwith the sliding sleeve that no torque is transmitted to .the disk butthat the sliding sleeve is axially displaceable on the armature shaft bymeans of at least one electromagnet acting upon the disk. In this case,at least one spring'acts on the disk connected with the sliding sleeveand arrests the hollow rotor in one of the possible two positions, i.e.,operating position and braking position, whilethe hollow rotor is movedinto the other of the possible two positions by an electromagnetcounteractingthe spring force and kept there. During the braking action,part of the internal wall of the flange connecting the tubular windingsupport with the sliding sleeve is pressed against the frontside of thestationary armature core. In another modification of the electric motorthe winding support and the stationary armature core are conical and atleast part of the lateral conical area of the stationary armature coreis used as the braking area. I

In fabricating a winding support of an electric motor with a hollowrotor it is advisable to proceed in such a 1 way that groovescorresponding to the arrangement of the windings are made in the outsideof a tube and such an amount of material is machined off the inside ofthe tube that the arrangement of the'windings still withstands therequired mechanical stress. Attachment, resin casting and baking of thewinding may be carried out either before or after machining of theinside ofthe tube.

For groove formation and for increasing the mechanical stability,mechanical webs are put on a thin-walled tube by one of the methods ofhard surfacing, welding, soldering, metal bonding. In this process, theexpense involved in finishing of the interior of the tube can be reducedconsiderably of eliminated entirely.

Especially with larger motors it may be advantageous to cast the windingsupport and use a casting material consisting of a mixture of metalparticles and an electrically non-conductive binder. If the right typeof metal particles are used, this material has a relatively highpermeability and a practically infinitely high electrical resistivity.Similar advantages are offered by winding supports pressed out of metalpowder and sintered afterwards. Of course, the winding supports can bemade either with or without grooves.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED IEMBODIMENTS In FIG. 1, the armature winding 1 is inserted into groovesof a winding support 2 and firmly connected with it through casting withsynthetic resin. On the side facing the collector 3, the winding supportis designed as a flange 4 which connects it with the shaft 5. The boreof the winding support in partly filled by a hollow cylindricalstationary armature core 6 which is attached to the steel tube casing 8by means of a screwed connection 7. On the collector side, the casing isclosed by the bearing plate 9. I

The bearing plate and the casing are indirectly connected witheach otherthrough a lock washer 10, a washer 11 made of insulating material, andscrews 12. The washer ll of insulating plastic material carries theholders 13 of the carbon brushes 14. Electric connections are carriedthrough a bore 15. The bearing plate FIG. 2 is an axial section througha motor with a hol-' low rotor, a braking device and cooling channels.The upper half of the diagram represents a cylindrical winding support,the lower half a conical winding support as one other possible type ofwinding support.

The cylindrical armature winding 1 is inserted into grooves of acylindrical winding support 2 or a conical armature winding 19 intogrooves of a conical'winding support 20 and firmly connected with itthrough casting with plastic resin. The winding support, irrespective ofits shape being cylindrical or conical, is designed as a flange 21 onits side facing the collector 3 and is connected with the sliding sleeve22 through this flange. The sliding sleeve is equipped with guidingelements engaging into the corresponding guiding elements of thearmature shaft 23 and allowing an axial displacement of the sleeve and,at the same time, a transmission of torque to be carried out. Also thecollector 3 is firmly connected with the sliding sleeve 22. Moreover,the sliding sleeve carries a control disk- 25 on the side facing awayfrom the winding support through a ball bearing 24 which can be loadedaxially,'which control disk can be moved axiallyby a spring 26in onedirection and an electromagnet 27 in the other direction.

' The bore of the cylindrical winding support 2 is filled with a hollowcylindrical stationary armature core 6a or, in the case of a conicalwinding support 20, with an essentially hollow cylindrical armature core28 which,

however, is conical on the outside, in such a way as to leave only anarrow air gap between the winding support and the armature core.

The spring 26 forces the winding support 2 against the frontside 29 ofthe'armature core 6a (braking position the electromagnet 27 counteractsthe spring and moves the hollow rotor into the operating position. In aconical arrangement, the spring and the electromagnet act in the sameway. However, in the braking position, the conical shell areas of thewinding support 30 and of the armature core 3l are forced upon eachother. Y

Of course, it is possible also to arrange the spring and theelectromagnet in such a way that the braking position is attainedthrough excitation of the electromagnet. Another possibility is thedistribution of several springs and several electromagnets on thecircumference of the control disk.

As can be seen also from the radial section AA in FIG. 3, four axialbores 32 are made in the armature corev6a and 28, respectively, as closeas possible to the I shell surface facing the winding support whichbores are connected with each other on. the front side facing thecollector 3 by means of a radial annular channel 33.

A disk is attached to the other front side of the armature core by ascrewed connection 34. Two channels 36 are machined into the surface ofthat disk facing the armature core which connect two each of the bores32 with each other. Moreover, two radial bores 37 are made in the disk35 each of which ends in one eachof the channels 36 and to which thecoolant inletline 38 and the coolant outlet line 39, respectively, areconnected. A flat seal 40 is installed between the armature core and thedisk 35 for watertight connection of the cooling channels.

The disk 35 also connects the armaturecore with the exciting core 42 bymeans of a screwed connection 41 which exciting core accomodates theexciting winding 17 and, at the same time, constitutes the motor casing.

Cooling channels 43, 44 of rectangular cross section are arranged on theperiphery of the exciting core and surround the core like a douplethread. As is evident from FIG. 4, the coolant flows in a clockwisedirection in channel 43 and in a counter-clockwise direction in channel44. Channels 43 and 44 are connected with each other by channel 45 onthe collector side in such a way that the cooling water flows through aninlet channel 46 into channel 43, from here on into the connectingchannel 45 and via channel 44 into the outlet channel 47.

On the collector side, the motor is closed with the bearing plate 9. Thebearing plate and the exciting core 42 serving as a casing are connectedwith each other indirectly through a lock washer 10, a washer 48 ofinsulating material, a screw 12. The washer 48 carries the holders 13 ofthe carbon brushes 14. Electric connections are led through a bore 15.The bearing plate 9 and the armature core 6a and 28, respectively, areequipped with ball bearings 16 and 16a to, support the armature shaft23.

The advantages arising from the invention lie especially in the factthat the use of a winding support of higher stability permits highertorques to be transmitted from the winding to the armature shaft. At thesame time, the winding support improves the stability of shape of thewinding. This higher stability of shape allows a reduction of the airgap to be made whose effective value is further reduced through the useof a winding support made of a ferromagnetic material. This results in amajor reduction of the exciting losses and, hence, a higher useful fluxand higher torque at the same amount of excitation.

Moreover, the winding support according to the invention permits higheroperating temperatures and thus a better ultilization at the samecomponent size. The resistance to gamma radiation is also increasedconsiderably with metallic winding supports, because the mechanicalstability is no longer dependent on a hardly radiation resistant plasticmaterial.

Moreover, quietness of operation is greatly enhanced which is importantespecially at low speeds in many areas of application.

Another advantage of the invention is the fact that the winding support,becauseof its stability, can be used to generate brake torque and thebraking devices are able to act direct upon the winding support. Theheat this generates is removed via the metallicwinding support. Thiseliminates the need for special brake disks to be attached to thearmature shaft, which would increase the moment of inertia.

The provision of cooling channels in the ferromagnetic core of theexciting winding and in the armature core adjacent to the armaturewinding also permits a much better ultilization of the windings which,under otherwise unchanged conditions, allows a tenfold increase in'motor power/Moreover, the increase in currentcarrying capacity leads toa further reduction of mass and thus of the moment of gyration of therotor.

We claim':

1. An electric motor of the double air. gap type for producing high'rated torques and high accelerations with low inertial moment comprisinga stationary armature core; a stationary exciting core; an excitationwinding associated with said exciting core; an armature shaft; adisplacement sleeve on said armature shaft, said displacement sleevebeing displaceable with respect to said armature shaft in an axialdirection; a thin walled winding carrier having a frontal face in theform of a flange connected to said displacement sleeve; an armaturewinding positioned on said winding carrier; an axially loadable bearingmeans; a non-rotatable control disk connected to said displacementsleeve via said bearing means for transferring axial movements of saidcontrol disk to said displacement sleeve; and nonrotatable meansseparate and distinct from the excitation winding and the armaturewinding for axially moving said disk from a first position in which itpositions said winding carrier in its operating position to a secondposition in which it positions said winding carrier in a brakingposition in which at least a portion of said winding carrier contactssaid armature core.

2. Ari electric motor as defined in claim 1, wherein said windingcarrier'is constructed from a material having a relative magneticpermeability s substantially greater than i and alow electricconductivity and eddy current loss.

3. An electric motor as defined in claim 2 wherein the material of thewinding carrier comprises sintered metal particles. I

4. Ari electric motor as defined in claim 2 wherein the material of thecarrier is a mixture of metal particles and an electricallynon-conductive binder.

5. An electric motor as defined in claim 1 further comprising coolingfluid channels within said exciting core and within said armature corefor removing heat produced by said exciting winding and said armaturewinding while maintaining the air gaps of the motor free of coolingfluid.

6. An electric motor as defined in claim 1, further including a motorhousing and wherein said means for axially moving said disk comprisesatleast one electromagnet fastened to said motor housing and at least onespringcoupled between said motor housing and said control disk.

7. An electric motor as defined in claim 6, wherein said at least oneelectromagnet in its energized state positions said control disk in thefirst position and said at least one spring urges said control'disktoward the second position in which it positions said winding carrier inthe braking position.

8. An electric motor as defined in claim 6, wherein said at least onespring urges said control disk toward the first position and said atleast one electromagnet in its energized state positions said controldisk in the second position in which it positions said winding carrierin the braking position.

9. An electric motor as defined in claim 1, wherein said stationaryarmature core includes a free frontal face developed as a brakingsurface and said flange of said winding carrier contacts said freefrontal face in the braking position.

10. An electric motor as defined in claim 6, wherein said stationaryarmature core includes a free frontal face developed as a brakingsurface and said flange of said winding carrier contacts said freefrontal face in the braking position.

11. An electric motor as defined in claim 7, wherein said stationaryarmature core includes a free frontal face developed as a brakingsurface and said flange of said winding carrier contacts said freefrontal face in the braking position.

12. An electric motor as defined in claim 1, wherein said windingcarrier and said stationary armature core are conical, at least aportion of the lateral surface of said armature core contacting saidwinding carrier during braking.

13. An electric motor as defined in claim 1, further comprising a motorhousing including bearing supporting means, wherein said stationaryarmature core is in the form of a hollow cylinder with a frontal faceand having cooling channels disposed in the vicinity of its periphery inthe direction of its longitudinal axis, said cooling channels beingconnected together by an annular channel in the vicinity of said frontalface; and further comprising two arcuate cooling channels in the form ofportions of a circular arc in said bearing supporting means into whichsaid cooling channels in said armature core open thereby combining theminto two groups, and two radial channels in said bearing supportingmeans which open into said arcuate cooling channels for feeding in andremoving the coolant.

14. An electric motor as defined in claim 1 wherein said exciting coreis a cylindrical exciting core with two frontal faces and having coolingchannels disposed at its periphery in the form of a double threaddefining a first passage and a second passage; and further comprising anintake line for coolant connected to said first passage at one of saidfrontal faces, a discharge line for coolant connected to said secondpassage at said one frontal face, and an annular channel at the otherfrontal face of said exciting core for connecting said cooling channels.

1. An electric motor of the double air gap type for producing high ratedtorques and high accelerations with low inertial moment comprising astationary armature core; a stationary exciting core; an excitationwinding associated with said exciting core; an armature shaft; adisplacement sleeve on said armature shaft, said displacement sleevebeing displaceable with respect to said armature shaft in an axialdirection; a thin walled winding carrier having a frontal face in theform of a flange connected to said displacement sleeve; an armaturewinding positioned on said winding carrier; an axially loadable bearingmeans; a non-rotatable control disk connected to said displacementsleeve via said bearing means for transferring axial movements of saidcontrol disk to said displacement sleeve; and non-rotatable meansseparate and distinct frOm the excitation winding and the armaturewinding for axially moving said disk from a first position in which itpositions said winding carrier in its operating position to a secondposition in which it positions said winding carrier in a brakingposition in which at least a portion of said winding carrier contactssaid armature core.
 2. An electric motor as defined in claim 1, whereinsaid winding carrier is constructed from a material having a relativemagnetic permeability Mu substantially greater than 1 and a low electricconductivity and eddy current loss.
 3. An electric motor as defined inclaim 2 wherein the material of the winding carrier comprises sinteredmetal particles.
 4. An electric motor as defined in claim 2 wherein thematerial of the carrier is a mixture of metal particles and anelectrically non-conductive binder.
 5. An electric motor as defined inclaim 1 further comprising cooling fluid channels within said excitingcore and within said armature core for removing heat produced by saidexciting winding and said armature winding while maintaining the airgaps of the motor free of cooling fluid.
 6. An electric motor as definedin claim 1, further including a motor housing and wherein said means foraxially moving said disk comprises at least one electromagnet fastenedto said motor housing and at least one spring coupled between said motorhousing and said control disk.
 7. An electric motor as defined in claim6, wherein said at least one electromagnet in its energized statepositions said control disk in the first position and said at least onespring urges said control disk toward the second position in which itpositions said winding carrier in the braking position.
 8. An electricmotor as defined in claim 6, wherein said at least one spring urges saidcontrol disk toward the first position and said at least oneelectromagnet in its energized state positions said control disk in thesecond position in which it positions said winding carrier in thebraking position.
 9. An electric motor as defined in claim 1, whereinsaid stationary armature core includes a free frontal face developed asa braking surface and said flange of said winding carrier contacts saidfree frontal face in the braking position.
 10. An electric motor asdefined in claim 6, wherein said stationary armature core includes afree frontal face developed as a braking surface and said flange of saidwinding carrier contacts said free frontal face in the braking position.11. An electric motor as defined in claim 7, wherein said stationaryarmature core includes a free frontal face developed as a brakingsurface and said flange of said winding carrier contacts said freefrontal face in the braking position.
 12. An electric motor as definedin claim 1, wherein said winding carrier and said stationary armaturecore are conical, at least a portion of the lateral surface of saidarmature core contacting said winding carrier during braking.
 13. Anelectric motor as defined in claim 1, further comprising a motor housingincluding bearing supporting means, wherein said stationary armaturecore is in the form of a hollow cylinder with a frontal face and havingcooling channels disposed in the vicinity of its periphery in thedirection of its longitudinal axis, said cooling channels beingconnected together by an annular channel in the vicinity of said frontalface; and further comprising two arcuate cooling channels in the form ofportions of a circular arc in said bearing supporting means into whichsaid cooling channels in said armature core open thereby combining theminto two groups, and two radial channels in said bearing supportingmeans which open into said arcuate cooling channels for feeding in andremoving the coolant.
 14. An electric motor as defined in claim 1wherein said exciting core is a cylindrical exciting core with twofrontal faces and having cooling channels disposed at its periphery inthe form of a double thread defining a firsT passage and a secondpassage; and further comprising an intake line for coolant connected tosaid first passage at one of said frontal faces, a discharge line forcoolant connected to said second passage at said one frontal face, andan annular channel at the other frontal face of said exciting core forconnecting said cooling channels.